1. Field of the Invention
The present disclosure relates to liquid crystal display (LCD) devices, and more particularly relates to an apparatus and method for driving a LCD device.
2. Description of the Related Art
Liquid crystal display (LCD) devices are devices for displaying an image by appropriately adjusting the transmissivity of liquid crystal cells depending on the type of an image signal. The transmissivity of a liquid crystal material may change according to the arrangement of liquid crystal molecules generated when an electric field is applied to the liquid crystal material.
Specifically, the arrangement of liquid crystal molecules varies over a long period of time. Due to such time delay, a moving image may suffer from tailing, blurriness, or a low dynamic contrast ratio or may look as if it was seen through a stroboscope when displayed by an LCD device.
In order to solve this problem, a response time compensation (RTC) method has been suggested. The RTC method is an LCD driving method that improves and compensates for the response speed of a liquid crystal material using an overshoot so that the liquid crystal material can quickly respond to a driving signal within 1 frame.
FIG. 1 is a graph comparing the LCD driving signals before and after compensation of the response speed of an LCD device using the RTC method. Referring to FIG. 1, Gn is an LCD driving signal yet to be compensated for, and Gn′ is an LCD driving signal compensated for using an overshoot.
In a case where the response speed of an LCD device has not been compensated for, the output level of a liquid crystal material changes in response to the LCD driving signal Gn. In this case, the liquid crystal material cannot reach a desired output level within one frame.
On the other hand, in a case where the response speed of the LCD device has been compensated for using an overshoot, the output level of the liquid crystal material changes in response to the compensated LCD driving signal Gn′. In this case, the liquid crystal material can reach a desired output level within one frame.
The above-mentioned LCD driving method that compensates for the response speed of an LCD device using an overshoot is called an LCD overdriving method. In a conventional LCD overdriving method, an LCD device is driven by comparing gray values of pixels of a current frame of a moving image with gray values of pixels of a previous frame of the moving image and then adding/subtracting an overshoot value to/from the gray values of the pixels of the current frame based on the comparison results.
The overshoot value is determined in consideration of the characteristics of a panel of the LCD device and is stored in a lookup table (LUT). The LUT is comprised of a plurality of overshoot values determined based on a result of comparing gray values of pixels of a current frame with gray values of pixels of a previous frame.
FIG. 2 is a block diagram of a conventional apparatus 200 for driving an LCD device. Referring to FIG. 2, the conventional apparatus 200 includes a storage unit 210, a LUT unit 230, and a calculation unit 250. The storage unit 210 stores pixel data of consecutive frames of moving image data (i.e., RGB data) output from a central processing unit or a baseband processing unit.
The LUT unit 230 includes a LUT, which is comprised of a plurality of overshoot values determined according to the characteristics of a panel of an LCD device. Pixel data Gn of a current frame of input moving image data and pixel data Gn−1 of a previous frame of the input moving image data, which is stored in the storage unit 210, are input to the LUT unit 230.
The LUT unit 230 reads and outputs one of the overshoot values of the LUT based on the pixel data Gn and the pixel data Gn−1. The calculation unit 250 compensates for the pixel data Gn by adding/subtracting the overshoot value output from the LUT unit 230 to/from the pixel data Gn and outputs the compensated pixel data Gn to a source driving unit (not shown).
As described above, a conventional LCD driving apparatus using the RTC method can compensate for the response speed of an LCD device, such as an LCD TV or a video game device, within one frame and thus can improve the quality of a moving image displayed by the LCD device. Unfortunately, the conventional LCD driving apparatus using the RTC method is only applicable to large-sized or line-powered LCD devices such as an LCD TV or a video game device, and cannot be practically applied to a small-sized or battery-powered LCD device, which includes a small-sized driving chip, and that is more sensitive to variations in the price of driving chips and consumption current.